Electrochemical elements such as batteries and accumulators are nowadays used in many fields. They are employed, in particular, for supplying portable appliances with electric energy. In very small appliances such as watches and hearing aids, the electrochemical elements are preferably used in the form of button cells. Hearing aids, in particular, have very high power consumption. Among modern hearing aids, a distinction is made between “behind the ear” devices (bte) and “in the ear” devices (ite) and canal devices which are used directly in the hearing canal. The power consumption of these devices depends, in particular, on the amplifier power. Higher-value devices additionally have microcomputers and transmission devices integrated into them, and these likewise have to be supplied with electric power.
Owing to the high power consumption, hearing aids are generally supplied by batteries of the electrochemical system zinc-air which have a particularly high capacity. Zinc-air button cells are essentially available commercially in four different sizes (in accordance with the standard IEC 60086-2). Hearing aids can generally be supplied with energy for from 3 days to 3 weeks when using zinc-air batteries in standard sizes.
Zinc-air batteries are not rechargeable and have to be disposed of appropriately after use. However, this is problematic since they contain about 1% by weight of mercury which should not get into the environment. In addition, the long-term use of a hearing aid is accordingly associated with high costs. For this reason, rechargeable batteries are increasingly being demanded. Among these, nickel-metal hydride batteries are particularly suitable since these have the same voltage as zinc-air batteries and a high current can be drawn from them. However, they have a very low capacity compared to zinc-air batteries. The maximum operating time of nickel-metal hydride batteries in the four sizes mentioned above is generally less than 1 day, so that they have to be recharged or replaced very frequently.
It could therefore be helpful to provide rechargeable batteries, in particular for hearing aids, which have a higher capacity than comparable known batteries. In addition, the batteries should also have an excellent cycling stability.